Electromyography (EMG) is an electrophysiological method in neurological diagnostics, in which the electrical activity of muscles is measured. Superimpositions of the action potentials of many muscle fibers as well as of changes thereof are often detected by means of concentric surface electrodes. Individual muscle fibers can also be detected with special needles, and measurements of the changes of potential differences on the skin are also possible with surface electrodes. The electrical activities, which originate, as a rule, from different muscles, are detected during the performance of an EMG.
As soon as a muscle contracts, this is detected on the basis of action potentials. If an EMG is carried out while a patient is being ventilated, it should be borne in mind that the patient is active in respect to his respiratory muscles, as long as he is breathing spontaneously at least partially. The patient must not be ventilated mandatorily in these cases, but the ventilation, especially the ventilator, must be synchronized with the spontaneous activity caused by the effort of the respiratory muscles.
Besides the use of electromyography to recognize myopathies and neuropathies, a system for assisting the mechanical ventilation of a patient is known, in which EMG signals are used. In a NAVA® system (Neurally Adjusted Ventilatory Assist), the ventilator is controlled as a function of the electrical activity of the diaphragm (Edi), which is detected by means of a special gastric catheter. Ventilatory assist, which takes place synchronously and proportionally to the patient's respiratory demand, is achieved here by varying the respiratory pressure generated by the ventilator, taking into account the amplitude and duration of the activity of the diaphragm (Edi). The patient's respiratory activity shall be assisted with this system by the ventilator assuming a necessary part of the respiratory work and thus ensuring that the patient is not needlessly exhausted or becomes tired. In view of the increase of chronic lung diseases and the need for improved therapy, such a ventilatory assist with improved interaction between patient and ventilator drive is an important requirement on modern ventilation systems.
Respiratory monitoring as well as ventilation control, especially ventilator control, based on signals of a surface EMG, are known as well. Such an EMG measuring system usually has an EMG front end, which is unidirectionally connected with a display, diagnostic or therapeutic device via a galvanic, wireless or optical signal connection.
A ventilation system for the non-invasive ventilation with a ventilator, which is controlled by a control unit, and with a patient module with electrodes for deriving electrode signals from the signal of a patient's chest, is known from DE 10 2012 003 509 A1. The control device according to the technical embodiment described is designed such that ECG signal components are suppressed in the electrode signals in order to obtain the electromyographic signals (EMG signals) representing the respiratory effort and to control the ventilator drive as a function of these EMG signals. It is thus possible by means of the technical means for accomplishing the object of the invention described to derive EMG signals from the electrode signals obtained, and to take these into account during the mechanical ventilation of a patient, on the one hand, and to record ECG signals and to make data representative of the ECG available for display, on the other hand.
Furthermore, EP 2 371 412 B1 discloses a ventilation or anesthesia system, which is coupled with an EMG measuring system, wherein signals, which are used as the basis for the mechanical ventilation, are provided by the EMG measuring system or a control device of this system. The control unit of the EMG system has an analog-digital conversion unit here, with which analog electromyographic muscle activity detected by the at least one sEMG sensor can be converted into digital signals. Since the at least one sensor detects only very low voltages from the respiratory muscles, so that the corresponding low voltages may be distorted when these very weak currents are being sent over rather great distances to an external control unit, a corresponding conversion already in the control unit arranged close to the patient is useful. The control device of the EMG measuring system can be identified by a higher-level control device, which is arranged especially within the ventilator. Suitable identification data are stored for this in the EMG front end.
The EMG front end modules arranged close to the patient, which are known from the state of the art, thus often have components for the digitization, preprocessing and transmission of the EMG signals as well as for supplying the module with energy. Furthermore, elements for signal processing are provided, e.g., for forming the difference, filtering, removing artifacts, above all of the electrical cardiac activity (ECG), and for calculating the enveloping curve. However, the drawback of the prior-art EMG front end modules is that a plurality of functions for measurement, signal processing, signal transmission, generation of control signals and for displaying measured values and of values derived therefrom are distributed among different medical devices.
On the one hand, many different devices are thus often arranged, especially in intensive care, and, on the other hand, the complexity of the overall system and hence of the possible source of risk during the wiring of the devices as well as the analysis of corresponding measured values is increased hereby. Likewise, the effort for the maintenance and verification of such systems with their different components is also relatively complicated.
Thus, a large number of parameters have had to be hitherto neglected or entered separately on a conventionally unidirectionally connected EMG front end module for cardiorespiratory analysis or for signal generation for controlling the ventilation. All the information is potentially available if the EMG functionality is integrated in the control unit of the ventilator, as is known from the state of the art; however, there arises the disadvantage of a self-contained device. As a result, the flexibility, especially the usability of the EMG functionality for patient monitoring, is reduced or simply impossible. Such a central structure also has disadvantages concerning the possibility of maintenance and software complexity.